The junction temperature of IGBT devices in semiconductor modules during operation in, for example, a power electronic converter, is an important parameter that provides information about the thermal stress the device is exposed to. Hence, it can be used to predict and evaluate the ageing of the IGBT device as well as the power module and to estimate the remaining lifetime of the IGBT device.
It is known for the junction temperature of an IGBT device to be measured using standard temperature measuring techniques, such as using an infrared camera probing, a thermal couple inside the IGBT device package directly at or next to the IGBT semiconductor, or measuring the internal gate resistance of the IGBT device in order to obtain an indication of the device temperature. These techniques either involve direct access to the IGBT device package or require specially designed IGBT devices.
Furthermore, the inner IGBT device temperature can be simulated by measuring the temperature of a base plate or substrate by means of a temperature sensor and applying a detailed thermal network describing the thermal interactions in the device. The simulation is based on information on electrical quantities, such as voltage and current waveform, that are applied to the IGBT device, so that the IGBT temperature can be estimated.
Due to the delayed thermal response when the temperature is not measured directly at the semiconductor junction, the above methods for determining the temperature do not provide the required timely resolution and precision. Consequently, these techniques are not suitable for online measurement of the IGBT junction temperature, in particular, if the timely resolution should be at a frequency close to the control frequency of the IGBT device.